1. Field of the Invention
The present invention relates to Coriolis gyroscopes. More particularly, the invention pertains to a method for quadrature-bias compensation in a Coriolis gyro, and to a Coriolis gyro which is suitable for such purpose.
2. Description of the Prior Art
Coriolis gyros (also referred to as “vibration gyros”) are increasingly employed for navigation. Such devices include a mass system that is caused to oscillate. The mass system generally has a large number of oscillation modes, initially independent of one another. A specific oscillation mode of the mass system is artificially excited to operate the Coriolis gyro. Such mode is referred to in the following text as the “excitation oscillation”.
Coriolis forces occur that draw energy from the excitation oscillation of the mass system when the Coriolis gyro is rotated and transmit a further oscillation mode of the mass system (referred to below as the “read oscillation”). The read oscillation is tapped off to determine rotations of the Coriolis gyro, and a corresponding read signal is investigated to determine whether any changes have occurred in the amplitude of the read oscillation which represent a measure of rotation of the Coriolis gyro.
Coriolis gyros may comprise either an open-loop or a closed-loop system. In a closed-loop system, the amplitude of the read oscillation is continuously reset to a fixed value (preferably zero) via respective control loops, and the resetting forces measured.
The mass system of the Coriolis gyro (referred to below as the “resonator”) may be of widely differing designs. For example, it is possible to use an integral mass system. Alternatively, it is possible to split the mass system into separate oscillators coupled to one another via a spring system and capable of movements relative to one another. For example, it is known to use a coupled system comprising two linear oscillators (also referred to as a “linear double-oscillator” system). When such a coupled system is used, alignment errors of the two oscillators with respect to one another are unavoidable due to manufacturing tolerances. The alignment errors produce a zero error component in the measured rotation rate signal, the so-called “quadrature bias” (more precisely, a quadrature-bias component).
Methods such as those disclosed, for example, in U.S. patent application publication 2003/061877. International patent publication WO 03/058167 and U.S. Pat. 6,067,858 are used to compensate for the quadrature bias. Alternating forces are used to compensate for the quadrature bias in this method.